I really know nothing about this area, but recently was talking to an American pilot who operates an Experimental Category aircraft (a small homebuilt jet, no kidding) and he said he can get it approved as a Permit plane in Spain. And that this will give him parking/overflight rights for the rest of Europe.
I know this man quite well; he's not a mug, is a brilliant engineer, pays a lot of attention to detail, and flies to Europe quite a bit. So this avenue is worth checking out.